NASA says evidence for 'Planet Nine' is mounting
October 18, 2017 at 07:00 AM EDT
We might not actually know how many planets are in our Solar System — and no, this isn’t a trick regarding Pluto’s status. For years, scientists have wondered if there might be a larger, planet-sized body lurking in or around the thick layer of debris called the Kuiper Belt, and now NASA is saying the evidence is hard to ignore.